SEISMIC INVESTIGATION OF NEAR-SURFACE GEOLOGICAL STRUCTURE IN THE PADUCAH, KENTUCKY, AREA - APPLICATION TO EARTHQUAKE HAZARD EVALUATION

Seismic methods were used to evaluate shallow geological conditions at 33 sites in the vicinity of Paducah, Kentucky. A combined set of P- a nd S-wave seismic refraction and reflection soundings were used, in ad dition to local borehole information, to produce structure maps of (1) a shallow (< 30 m deep) horizon believed to represent an unconformity surface at the top of the Eocene, and (2) the Paleozoic bedrock surfa ce (<85 to > 160 m deep). Shear-wave velocity contrasts across the sha llow unconformity were generally 2-to-1 while the contrast at the top of the Paleozoic bedrock exceeds 5-to-1. These seismic boundaries have been determined to be very important in modelling and interpreting ea rthquake ground motion amplification in the Paducah area. The quality and accuracy of the data, and the cost-effective nature of the methods , suggest that other communities in areas at risk to damage from seism ic activity, with foundation conditions comparable to Paducah, might b enefit from similar characterization in order (1) to identify seismica lly hazardous, near-surface, geological conditions, and (2) to develop geological models that could be used in computer simulations of site response.